The present invention relates to a method of polishing the irregular front of a wafer or semiconductor substrate, and a device therefor. More particularly, the present invention is concerned with a wafer polishing method which polishes the front of a wafer while holding the rear of the wafer in close contact with a backing, and a device therefor.
It is a common practice with a semiconductor production line to polish and thereby flatten the irregular front of a wafer or semiconductor substrate which is ascribable to a diffusing step. This kind of polishing is comparable with mirror polishing used to polish a semiconductor substrate produced by slicing a semiconductor crystal member. However, these polishing schemes are noticeably different from each other when it comes to the required polishing ability. Although mirror polishing attaches importance to surface roughness, control of the order of microns suffices as to the amount of polishing of the crystal substrate and the distribution of polishing in a plane. By contrast, the amount of polishing and the distribution thereof in a plane are critical with the other polishing scheme, i.e., flattening, and must be controlled by the order of tens to hundreds of angstroms. Further, because cleaning to follow mirror polishing is free from strict limitations, a broad range of cleaning liquids are usable. In the case of the polishing following the diffusing step, only a limited group of cleaning liquids are usable because films of various substances exist on the wafer beforehand. It has been customary with this kind of polishing or flattening to use mechanical cleaning relying on a brush scrubber.
While various kinds of approaches have been proposed in the past in order to flatten the irregular front of the wafer by polishing it, they cannot provide the front with a sufficient degree of evenness and make it difficult to remove particles in the cleaning step to follow the polishing step.